Karachun V.V., Mel’niсk V. N.

National Technical University of Ukraine «KPI»

Mass-Exchange and Aeration in Bioreactors

Recently in microbiological, food and medical industries it appeared a numerous number of different technical decisions on construction of reactors for aerobic growth of biomass and receiving its metabolits. At last two centuries it was received more than three hundred of patents on these constructions. The situation that formed can be explained not only by necessity of production, but by priority interests of wide general public of researchers, that see of this field.

Plant cells, which have cell wall, and cultures of living cell of animal and man, that do not have, accordingly growing up on the equipping with their specific, corrected instrument features of biotechnological processes. Hence it appears, either high-speed mechanical means of mass-exchange, or contrary – low-speed, without available components of big drawl, frictional and toothed pairs, clutches etc.

The effectiveness of bioreactors is defined by many factors. But the principal of them are used to be the qualitative characteristics of processes of mass-exchange and aeration. The technical decisions of features of constructions of biotechnological equipment are thus subjected to one point – exclusion of risk of appearing of gradient manifestation of these components in polyaggregate structure. The solution of problem serves as subsoil of growth of quality indexes of technological process.

Authors suggest patent-defended technical realizations for apparatus for cultivation of calls with the aim of decision the nagging problems of one of the priority field of development of contemporary state – biotechnology.

Logic of improvement of construction of bioreactors is completely opportune for chemical reactors.

For organization of industrial producing of materials of biological origin, it is utterly necessary the knowledge of chemical technology, biochemistry, microbiology etc. The valuing of the generally recognized contents of production in different fields of industry affirms that big number of processes about their essence is only the new method of approach to use the methods, which are widely used in industry. Thus the achievements of chemical producing may be used in biochemical technology. It is possible to make a couple of interesting comparisons of chemical and biochemical technologies.

1. The main conformities of mass-exchange and energy-exchange, as the concentration of stream of liquid, are general, but with the difference that the productions with treatment of biological processes have deal with narrow temperature diapason and rather often with viscous Newtonian fluid.

2. Many methods, such as filtration, found wide application in biochemical technology.

3. Numerous methods are connected with supporting the demands of sanitary-and-hygienic clauses and realization of sterilizing operations. Zome of them may be qualified as new. These methods ground on using heat, different chemical substances and penetrating radiation of high intensity.

4. The ownership of biology fundamentals is necessary for every aspect of biochemical technology, because often it arise the necessity of struggle against strange micro flora, or with treatment of surprisingly sensitive and unstable materials, in particular, albumens and ferments.

5. Biochemical technology includes number of specific productions, which do not ground on specific qualification. The producing of vaccines, to the point, requires knowledge and skills in medical sphere, in particular, such an aspect, as culture of tissue.

To the sector of biochemical technology refers those fields of industry that are called to produce, manufacture and to keep the materials of biological origin. Here it is necessary to refer processes of treatment the food products – bread-baking, preserving etc., fermentative productions – production of wine, beer, alcohol, acetone, butanol, and other resolvents, producing of yeasts, and also products of microbiological synthesis – antibiotics, vitamins, ferments, organic acids, bacterial defending preparations, steroids, growth accelerators etc.

The important role in biological systems plays heat- and mass-exchange through the surfaces of phase disengagement. Generally, these processes fulfil classic laws; however often do not fulfil usual conceptions.

Sometimes specialists on biochemistry have to slow down or to stop processes, which living organisms take part in, and sometimes – to accelerate them. Thus, in many cases of cultivating of microorganisms it happens the destruct all the collateral microbes to secure optimal conditions of growth of chosen species.

In process of chemical-technology operations substances undergo transformation, which have their own, immanent only them, physic-chemical properties. The nature of chemical interaction is many-sided. Naturally, the number of chemical reactors fulfils this variety. However, in specialized literature it is practically absent any satisfactory classification of chemical reactors, in case of bearing in mind non-constructive features of apparatus, but inner essentiality of processes, their ideology, characterized by concrete defined connection of physical and chemical phenomenon.

Really, the same reaction may be realized in the cascade of apparatus with mixers and in the columns. The apparatus, in which the reaction realizes, may be bubble, attachment-type, rotor-type or plate-type. As reactor it may be used one of the numerous constructions of contact apparatus. Although the construction of apparatus influences on rate of conversion and selectivity of process, its essentiality is characterized not with the construction of reactor but with definite interconnection of physical and chemical factors, necessary for successful running of reaction. The construction of apparatus is not only the mean of influence on this interconnection buy means of acceleration of individual physical or chemical stages.

It needs to be mentioned that technological parameters of process (temperature, pressure, setted rate of conversion etc.) often play role, analogous to role of the construction of reactor. But not always. Thus, the rise of temperature may put the system out of the zone of stratification into the homogeneous zone that substantially changes the inner matter of process. At once, the rise of pressure may lead to reverse transition.

Thereby, character of reactor work, demands to its work are defined not with construction and technological parameters, but in the first place with those physical processes, which ensures necessary demands of chemical interaction running. Exactly with these positions chemical reactors may be divided into three big groups: homogeneous, heterogeneous and heterogeneous-catalytic.

In homogeneous reactors process occurs in one phase and do not accompanies with phase-transfers. Leak of transference of substance or energy through the boundary of phases is the basic feature of homogeneous processes. At this it is not necessary reactor to contain only one phase. It can be filled with inert solid header for decreasing of the longitudinal mixing, either the inert fluid or gas-substance can be served in it for barbotage mixing or making the airlift. And with it, if in the reactor do not happen the exchange of substance or energy, it might be rating as homogeneous.

Reactionary phase in this case can be heterogeneous at its structure, temperature and concentration gradient may occur in it. Indeed, reactionary phase may exchange energy with the walls of reactor or with built-in heat-exchangers.

Homogeneous reactors can be liquid-phase and gas-phase. Heterogeneous reactors have two features. At first, interphase exchange of substance and energy (or both) happens, and firstly, solid catalyst is absent. The most widespread are heterogeneous reactors for systems liquid-liquid or liquid-gas. Rarely reactors for systems liquid-liquid-gas occur. Uniflow and counterflow, isothermal and non-isothermal reactors have their own features. However these discrepancies are not principle and do not serve as features of particular types of reactors. Some principal features have reactors in which phases exchange only energy. This type of reactors is the intermediate between homogeneous and heterogeneous. To the rank of heterogeneous, reactors of this type are rated in account of their computation needs calculation of interphase surface.